1. Field of the Invention
The present invention relates to a method of controlling ignition timing in an internal combustion engine, and more particularly to a method of controlling ignition timing in what is called a dual-injection-type internal combustion engine including an in-cylinder injector injecting a fuel into a cylinder and an intake port injector injecting a fuel into an intake manifold or an intake port.
2. Description of the Background Art
In general, what is called a dual-injection-type internal combustion engine including an in-cylinder injector injecting a fuel into a cylinder and an intake port injector injecting a fuel into an intake manifold or an intake port is known (for example, Japanese Patent Laying-Open Nos. 2001-020837, 05-231221, and the like), in which use of these injectors is switched in accordance with an operation state of the engine so as to realize stratified charge combustion in a low-load operation region and homogeneous combustion in a high-load operation region and so as to inject the fuel at a prescribed injection ratio in accordance with the operation state, for achieving improvement in fuel efficiency characteristic and output characteristic.
Generally in a fuel-injection-type internal combustion engine, in order to achieve appropriate combustion in accordance with the operation state, various corrective advance (or corrective retard) values in accordance with the state of the engine are added to a basic ignition timing value that has been set in advance in correspondence with the operation state and stored in a map or the like, so as to calculate final ignition timing. Based on that ignition timing, ignition is carried out and the engine is operated.
In the dual-injection-type internal combustion engine described above, there is a difference in a temperature in a combustion chamber due to a difference in the injection manner, between an injection manner where the fuel is injected from the in-cylinder injector and an injection manner where the fuel is injected from the intake port injector. Specifically, in the in-cylinder injection where the fuel is injected from the in-cylinder injector, as compared with port injection, the temperature in the combustion chamber is lowered as a result of a cooling effect of latent heat of vaporization of the fuel injected into the cylinder. Therefore, in a normal operation state in in-cylinder injection, an appropriate basic ignition timing value adapted to such a combustion chamber temperature is determined.
Meanwhile, in a transition operation such as switching of the injection manner from the intake port injector to the in-cylinder injector or change in an injection ratio, the cooling effect described above is not exhibited immediately and the combustion chamber temperature is higher than in the normal operation state, in which case knocking is likely.